FR3097592A1 - Constant volume combustion system with synchronized injection - Google Patents

Abstract

Constant volume combustion system with synchronized injection A constant volume combustion system (1) for a turbomachine comprises a plurality of combustion chambers (100) distributed annularly around an axis (XX '), each combustion chamber comprising an inlet port (102) and an outlet port (103), a selective closure element (200) movable in rotation with respect to the combustion chambers (100), the selective closure element comprising a ferrule ( 210) opposite the inlet and outlet openings (102, 103) of the combustion chambers (100). The ferrule (210) comprising on a first annular portion (211) at least one inlet port intended to cooperate with the inlet orifice (102) of each combustion chamber during the rotation of the closure element selective (200) and on a second annular portion (212) at least one exhaust port intended to cooperate with the outlet orifice (103) of each combustion chamber during the rotation of the selective shutter element. Each combustion chamber (100) includes a fuel injection device (140) whose opening and closing are synchronized by the shutter element (200). Figure for the abstract: Fig. 1.

Description

Constant volume combustion system with synchronized injection

The present invention relates to the field of combustion chambers of aircraft turbomachines, of the constant-volume combustion type. The invention applies to all types of turbomachines, in particular to turbojets, turboprops, and turbomachines with unducted fans, also known by the Anglo-Saxon term “Open Rotor”.

A conventional aircraft turbomachine comprises, in known manner, one or more combustion chambers. Such a combustion chamber is supplied with pressurized air by a compressor module and it comprises one or more fuel injectors which are capable of injecting fuel into the air flow admitted in order to burn it and thus cause the emission of gas which are used to drive a turbine, which in turn drives the compressor module and which may also drive a turbine engine fan.
In such a chamber, the fuel flow is continuous and the combustion operates according to a so-called Brayton cycle, that is to say according to a combustion cycle at constant pressure. Nevertheless, to obtain specific consumption savings, it has been envisaged to replace the combustion chamber operating according to a Brayton cycle by a plurality of combustion chambers operating according to a Humphrey cycle, that is to say according to a cycle Constant Volume Combustion or "CVC". Document WO 2016/120551 discloses a constant volume combustion module comprising combustion chambers arranged around an axis, each chamber comprising an inlet orifice or compressed gas inlet port and an outlet orifice or port for burnt gas exhaust, and a rotary intake/exhaust valve. Each inlet/outlet port is configured to be opened or closed by the rotary inlet/exhaust valve.

In this type of combustion module, the management of transfer and injection times determines the quality of the combustion process. Combustion efficiency has a direct impact on overall system efficiency. However, controlling fuel injection in constant volume combustion systems is tricky and complex to implement. There is therefore a need to optimize the management of fuel injection times and the synchronization with the other elements (inlet/outlet ports) in this type of system and to simplify its implementation.

To this end, the present invention proposes a constant-volume combustion system for a turbomachine comprising a plurality of combustion chambers distributed in an annular manner around an axis, each combustion chamber comprising an inlet orifice or inlet port and an outlet orifice or exhaust port, a selective shutter element movable in rotation around the axis relative to the combustion chambers, the selective shutter element comprising a ferrule facing the inlet and outlet orifices combustion chambers, the shroud comprising on a first annular portion at least one intake port intended to cooperate with the inlet orifice of each combustion chamber during rotation of the selective shutter element and on a second annular portion at least one exhaust port intended to cooperate with the outlet orifice of each combustion chamber during rotation of the selective shutter element, characterized in that each combustion chamber comprises a device for fuel injection whose opening and closing are synchronized by the shutter element.

The use of the same mechanical part, namely the obturation element, to ensure both the function of sequencing the openings and closings of air and of supplying fuel makes it possible to ensure effective synchronization between the times critical in the combustion system. The management of the injection times is optimized in relation to the combustion and exhaust times or phases, thus improving the efficiency of the combustion system.

According to a particular characteristic of the system of the invention, the fuel injection device comprises an injection valve present between a fuel supply circuit and a combustion chamber and a rocker arm configured to control the opening of the valve injection, the rocker arm cooperating with one or more injection cams present on the closure element to control the opening of the injection valve. This injection is carried out directly in the combustion chamber. By design, the injection cam allows both pressurization of the injected fuel and control of the quantity injected.

According to another particular characteristic of the system according to the invention, the latter further comprises an aerodynamic injection device configured to supply fuel to each combustion chamber in a synchronized manner via one or more injection orifices present on the element of shutter. This makes it possible to perform a function of carburizing the combustion chambers with small sizes of fuel drops without having to implement high levels of fuel pressure. It is thus possible to obtain savings in consumption compared to an injection only at high pressure.

The invention also relates to a turbomachine comprising an axial or centrifugal compressor and an axial or centripetal turbine, the turbomachine further comprising a combustion system according to the invention, the combustion system being present between the compressor and the turbine.

Another subject of the invention is an aircraft comprising at least one turboprop engine, the turboprop engine comprising a turbomachine according to the invention.

Figure 1 is a schematic view in longitudinal section of a turbomachine comprising a combustion system according to one embodiment of the invention,

Figure 2A is a schematic exploded perspective view of the combustion system of Figure 1,

Figure 2B is a detail view of Figure 2A showing combustion chambers,

Figure 3 is a schematic perspective view of the shutter element of the combustion system of Figure 1,

Figure 4 is a partial view in radial section of the combustion system of Figure 1 showing an aerodynamic injection in a combustion chamber,

FIG. 5 is another partial view in radial section of the combustion system of FIG. 1 showing direct injection into a combustion chamber.

The invention applies generally to a turbine engine comprising an axial or centrifugal compressor and an axial or centripetal turbine.

Figures 1, 2A and 2B illustrate a combustion system 1 in accordance with one embodiment of the invention. In the example described here and as represented in FIG. 1, the combustion system 1 is integrated into a turbine engine or turbine engine 10 for a turboprop, the combustion system being placed in the turbine engine downstream of an axialo-centrifugal compressor 11 and upstream of an axial turbine 12, the compressor 11 and the turbine 12 being interconnected by a system of shafts 13. The turbine 12 comprises a movable wheel 120 connected at its center to the system of shafts 13 and comprising at its outer radial end a plurality of blades 121.

The combustion system 1 comprises a plurality of combustion chambers, in the embodiment described here 10 combustion chambers 100, numbered 100 ₁ to 100 ₁₀ in the figure, distributed in an annular manner around an axis XX' defining a direction axial D _A . Each combustion chamber 100 is delimited by an enclosure 101, here of substantially parallelepipedal shape, a closed rear end 101b secured to the enclosure 101 and a cylindrical ring 110 on the outer face 112 of which the enclosure 101 is fixed for example by welding. , brazing, mechanical connection (screw-nut) or bonding when the enclosures 101 and the cylindrical ring 110 are made of metallic material. The cylindrical ring 110 and the enclosures 101 can also be made of ceramic matrix composite (CMC) material, that is to say a material formed from a carbon or ceramic fiber reinforcement densified by a matrix at least partially ceramic.

The cylindrical ring 110 forms the front bottom 101a of each combustion chamber which is located closest to the axis XX' in a direction opposite to the rear bottom 101b in a radial direction D _R . The cylindrical ring 110 comprises a first series of slots 113 each forming an inlet orifice or intake port 102 of a combustion chamber 100 and a second series of slots 114 each forming an outlet orifice or exhaust port 103 of a combustion chamber 100 (FIG. 2B). The front bottom 101a of each combustion chamber 100 thus comprises an inlet orifice 102 and an outlet orifice 103. The internal face 111 of the cylindrical ring 110, which comprises the inlet and outlet orifices of each combustion chamber combustion, is intended to be placed facing a shell of a selective shutter element described below in detail. The enclosures 101 of the combustion chambers extend from the outer face 112 of the ring 110 in the radial direction D _R .

The combustion system 1 also comprises a selective shutter element 200 movable in rotation about the axis XX' relative to the combustion chambers 100. The selective shutter element 200 comprises a ferrule 210 facing the orifices of entry and exit 102 and 103 of the combustion chambers 100. The shroud 210 is divided into a first annular portion 211 and a second annular portion 212 each extending over the entire circumference of the shroud 210 (FIGS. 2A and 3). The first annular portion 211 comprises at least one intake port intended to cooperate with the inlet orifice 102 of each combustion chamber 100 during the rotation of the selective shutter element 200. In the example described here , the first annular portion 211 comprises two intake ports 2110 and 2111 angularly offset by 180° along the first portion. The second annular portion 212 comprises at least one exhaust port intended to cooperate with the exhaust port 103 of each combustion chamber 100 during the rotation of the selective shutter element 200. In the example described here, the second annular portion 212 comprises two exhaust ports 2120 and 2121 angularly offset by 180° along the second portion. The start of each intake port 2110, 2111 is substantially angularly aligned with the start of each exhaust port 2120 and 2121 respectively, the exhaust ports extending over a greater circumferential length than the intake ports. The selective shutter element can be made of metallic material or CMC composite material.

The combustion system 1 further comprises a fixed intake guide 300 present inside the shroud 210 of the shutter element 200 on the side of the first portion 211 of the shutter element and a manifold fixed exhaust 400 which extends in an annular manner inside the ferrule 210 of the selective shutter element on the side and along the second portion 212 of said ferrule (FIG. 1).

The selective shutter element 200 is the only rotating element in the combustion system 1. In the example described here, it is driven in rotation by means of a drive shaft 233 (FIG. 1). During its rotation, the obturation element 200 will selectively open and close the inlet and outlet ports 102 and 103 of each combustion chamber in order to implement a combustion at constant volume according to the Humphrey cycle, c ie comprising a combustion time, an exhaust time, and a fresh air intake and burnt gas scavenging time.

According to the invention, each combustion chamber 100 each combustion chamber comprises a fuel injection device 140 whose opening and closing are synchronized by the shutter element 200. In the example described here, each fuel injection device 140 comprises an injection valve 141 present between a fuel supply circuit 142 and a combustion chamber 100 (FIGS. 4 and 5). Each fuel injection device 140 also includes a rocker arm 143 configured to control the opening of the injection valve 141. More specifically, the rocker arm 143 includes a tappet 1430 intended to cooperate with injection cams as explained below. after, a rocker arm rod 1431 extending the push rod 143 and a finger 1432 pivotally mounted around an axis 1433 and connected at one of its ends to the rocker arm rod 1431. The free end 1432a of the finger 1432 is in contact with the injection valve 141.

The closure element 200 comprises a plurality of injection cams 220 present here on the end of the first annular portion 211. The injection cams 220 are distributed over the outer surface of the shell 210 of the element. shutter 200 at determined locations in order to control the injection of fuel into each combustion chamber 100 at times synchronized with the Humphrey cycle implemented with the shutter element 200. In other words, the cams injection nozzles 220 are placed at angular positions on the shroud 210 of the shutter element so as to trigger the injection of fuel into a combustion chamber just before the initiation of a combustion phase therein .

The realization presented here of shutter systems (inlet/outlet orifices) by radial slots positioned on a cylindrical ring can also be obtained by discs pierced with axial slots. The two discs (inlet and outlet) are then mechanically linked, one of the two comprising the control system (cam) of the fuel injection rocker arm.

The operation of a fuel injection device 140 is illustrated in FIGS. 4 and 5. FIG. 4 shows the device 140 in the rest position, that is to say when the tappet 1430 of the rocker arm 143 is not not in contact with an injection cam 220. In this position, the free end 1432a of the finger 1432 does not exert pressure on the injection valve 141 which is held in its closed position by a return spring 1410 The rocker arm rod 1431 is housed in a guide sleeve 1434 also provided with a return spring (not shown in FIGS. 4 and 5) in order to maintain the rocker arm in the rest position.

In FIG. 5, the shutter element has moved into an angular position in which an injection cam 220 contacts the tappet 1430 of the rocker arm. In this position, the injection cam 220 pushes on the push rod 1431 which, by moving in the direction D1, causes the tilting of the finger 1432 and the application of a pressure force from its free end 1432a on the valve. injection valve 141. Injection valve 141 is then opened and fuel 150 from fuel supply circuit 142 can then be injected into combustion chamber 100.

Combustion can be initiated in known manner either by a spark igniter (candle) or by a gas thermal igniter (not shown in FIGS. 4 and 5). If conditions permit, combustion can also be initiated by exhaust gas recirculation, or EGR, as in a diesel engine.

The system of the invention is remarkable here in that the same part is used, namely the rotary shutter element, to control both the openings and closings in air of the combustion chambers and the injection of fuel. in this one. This ensures optimized management of the times or phases necessary for the implementation of the Humphrey cycle. In addition, the shutter element allows the fuel to be pressurized in the combustion chamber without having to use an external high-pressure pump.

According to an additional feature of the invention, the constant volume combustion system of the invention further comprises an aerodynamic injection device configured to supply fuel to each combustion chamber in a synchronized manner via one or more injection ports present on the shutter element. More specifically, as illustrated in FIGS. 4 and 5, an aerodynamic injection device 160 comprises an aerodynamic pre-carburation injection circuit 161 intended to cooperate with one or more injection orifices 162 present on the element of filling. In the example described here, the closure element 200 comprises two injection orifices 162 present on the first annular portion 211 of the ferrule 210 at angular positions allowing fuel to be injected into a combustion chamber just before the initiation of a combustion phase therein (FIG. 3). As illustrated in particular in FIG. 3, the injection orifices 162 correspond to openings which cooperate with the intake ports 2110 and 2111 and which are here offset from the latter in the axial direction D _A . An aerodynamic low pressure injection zone is thus defined which combines fuel injection with air intake. In this way, both fuel and air are injected into the combustion chamber. The speed of the air injected at low pressure makes it possible to atomize the injected fuel.

FIG. 4 illustrates an angular position of the shutter element in which the outlet of the aerodynamic pre-carburation injection circuit 161 is aligned with an injection orifice 162 common with the intake port 2110 which is itself even aligned with the inlet 102 of the combustion chamber.

In this position, circuit 161 is controlled to deliver an aerodynamic jet of fuel 170 into combustion chamber 100 via injection port 162. Aerodynamic injection consists of injecting an air/fuel mixture into the combustion chamber. The speed of the air admitted into the combustion chamber makes it possible to atomize the injected fuel.

In FIG. 5, the obturation element has moved into an angular position in which the outlet of the aerodynamic pre-carburation injection circuit 161 is no longer aligned with an injection orifice 162. This position corresponds at the time when fuel 150 is injected into the combustion chamber 100 by the fuel injection device 140 as previously described.

In the example described above, the injection device uses a rocker arm and an injection valve for direct fuel injection. However, other injection devices such as an electric valve injector, for example, can be used. In this case, the shutter element comprises means for controlling the activation of the solenoid valve as a function of its angular position. In general, any injection device capable of being synchronized with the closure element can be used.

In the system presented here, it is quite conceivable to provide the obturation element with several cam tracks making it possible to choose, according to operating needs, a determined fuel distribution sequence, on the same principle as the system with variable valve timing of a piston engine. In this case, the rocker arm will "read" one or other of the tracks of the cam system defining the injection sequence.

Claims (5)

Constant volume combustion system (1) for a turbomachine comprising a plurality of combustion chambers (100) distributed in an annular manner around an axis (XX'), each combustion chamber comprising an inlet port (102) and a outlet orifice (103), a selective shutter element (200) movable in rotation about the axis (XX') relative to the combustion chambers (100), the selective shutter element comprising a shroud (210 ) facing the inlet and outlet orifices (102, 103) of the combustion chambers (100), the shroud (210) comprising on a first annular portion (211) at least one intake port (2110) intended to cooperating with the inlet (102) of each combustion chamber during the rotation of the selective shutter element (200) and on a second annular portion (212) at least one exhaust port (2120) intended to cooperate with the outlet orifice (103) of each combustion chamber during the rotation of the selective closing element, characterized in that each combustion chamber comprises a fuel injection device (140) whose opening and closing are synchronized by the shutter element. System according to Claim 1, in which the fuel injection device (140) comprises an injection valve (141) present between a fuel supply circuit (142) and a combustion chamber (100) and a rocker arm (143) configured to control the opening of the injection valve, the rocker arm cooperating with one or more injection cams (220) present on the closure element (200) to control the opening of the valve 'injection. A system according to claim 2, further comprising an aerodynamic injection device (160) configured to supply fuel (170) to each combustion chamber (100) in a synchronized manner via one or more injection ports (162) present on the obturation element (200). Turbomachine (10) comprising an axial or centrifugal compressor (11) and an axial or centripetal turbine (12), the turbomachine further comprising a combustion system (1) according to any one of claims 1 to 3, the combustion system being present between the compressor and the turbine. Aircraft comprising at least one turboprop, the turboprop comprising a turbomachine according to claim 4.